On Fri, 2007-02-09 at 06:51 -0500, chrism@xxxxxxxxx wrote:
> hkclark@xxxxxxxxx wrote:
> > On 2/8/07, Johnny Hughes <mailing-lists@xxxxxxxxxxxx> wrote:
> >>
> >> It should not be a problem as lots of your memory used is buffers and
> >> cache.
> >>
> >> CentOS-3 is going to be supported for a while yet (EOL is scheduled for
> >> Oct 31, 2010), so if it is working perfectly and doing what they want,
> >> they may want to keep it though.
> >>
> >> If they upgrade or don't, the memory should be OK either way .
> >>
> >
> > Hi Johnny,
> >
> > Good info -- thanks. They have a small app they want to add that
> > requires a newer version of Perl than 5.8.0 that comes with CentOS 3.
> > Rather than getting into a non-RPM version of Perl, we were thinking
> > going to CentOS 4 would be easier and cleaner.
> >
> > In your experience, would you say that my "quick & dirty" measurement
> > of CentOS 4 needing 10-25 MB more memory than CentOS 3 (again, for a
> > non-X box with a minimal install) is accurate (at least in approximate
> > terms)? Or is there something I'm not taking into account -- e.g,
> > some of the libraries and/or other "basic server apps" such as apache
> > with PHP or MySQL will make that number much higher? Although this
> > box is doing OK on memory now, I would hate to kill their possible
> > expansion plans just because we did an upgrade and it sucked up way
> > more memory than we though.
> >
> > Again, thanks for all the great things you and the CentOS team are doing!
>
> Here is the output of "free" for 2 identical systems that happen to be
> running CentOS3 and CentOS4. The only difference is the CentOS4 system
> has 2GB RAM vs 1GB in the CentOS3 system.
>
> The CentOS3 system shows:
>
> total used free shared buffers cached
> Mem: 1024292 660572 363720 0 102612 397072
> -/+ buffers/cache: 160888 863404
> Swap: 2104464 0 2104464
>
>
> CentOS4 shows:
>
> total used free shared buffers cached
> Mem: 2074928 2030412 44516 0 276628 1365792
> -/+ buffers/cache: 387992 1686936
> Swap: 2104464 144 2104320
>
> As others have noted, a lot of the free RAM is just gobbled up as
> buffers and cache. As needed, the system will reallocate that memory so
> that your fancy perl application can get at it. :)
>
> Call me crazy, but I don't understand the agonizing fork in the decision
> tree here. RAM is ridiculously cheap. Why not just upgrade to 1GB
> while you're doing the 3-->4 upgrade? I suspect it isn't really needed,
> but it will add minimal cost to the operation (certainly much less than
> the cost of your time to accomplish the software update and test the new
> system).
>
RAM is indeed very cheep ... and having 1gb should be easy, I agree with
chris.
I also agree that as long as you have 200 mb free (as in your initial
post) that you should not have any problem shifting to CentOS-4.
When you use free ... anything that is in buffers and cache should be
subtracted if you really want to know how much (REAL/HARD) memory is in
use.
This is because the linux kernel fills up to the max all it's memory by
design. If you are not using it, it will cache stuff there. The theory
is that if you need that cached data again, it will be available in
memory and that you can switch out the buffers / cache cheaply when you
really need the memory.
So, in your initial post you had this:
total used free shared buffers cached
Mem: 511428 497956 13472 0 29868 178280
That means, I would call your hard memory used:
511428 - (29868+178280) = 303280
So ... moving from CentOS-3 to CentOS-4 should not be a major issue on
that machine.
(In your Centos-4 VM, subtract buffers/cache from used and see how that
looks)
Some of our CentOS machines have 512mb (they are donated machines and we
can't MAKE them have more memory). They work OK and serve between 1600
GB and 3200 GB per month via rsync and httpd, so certainly a web server
(if java is not involved :P) CAN work OK with 512mb RAM. 1 GB would be
MUCH better though.
Thanks,
Johnny Hughes
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